html,
body,
#app{
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
}
#app{
    padding-top: 30px;
}
  .red{
    background-color: red;
  }
  .ccc{
    background-color: #ccc;
  }
  .piece{
    width: 20px;
    height: 20px;
    border-radius: 50%;
    overflow: hidden;
  }
  .signBox{
      position: absolute;
      left: 200px;
      top: 200px;
  }
  .backOne,
  .beforeBackOne{
    font-size: 14px;
    margin: 15px;
    padding: 5px;
    box-shadow: 0 0 2px #000;
    border-radius: 3px;
    text-align: center;
    cursor: pointer;
  }